In oil field operations, reciprocating pumps are often used for various purposes. Reciprocating pumps utilize a plunger that reciprocates in and out of a pump housing to move fluid through a cavity defined by the pump housing. A motor rotates a crankshaft connected to the plunger to pull fluid into the pump cavity through a fluid intake and push fluid out of the pump cavity through a pump outlet. The plunger extends through a cylinder chamber of the pump housing to interact with the cavity. A seal in the cylinder chamber of the pump housing prevents leakage of fluid from around the plunger during pumping operations. Generally, a seal or packing assembly is composed of different types of seals to increase the sealing impact of the seal assembly. The seal assembly is disposed within a recess of the cylinder chamber.
In one type of seal assembly, a main seal or pressure ring is sandwiched between at least two other seal types. Generally the main seal will be formed of a pliable or rubber-like material. During operation, the seal assembly is compressed, causing the main seal to flair into contact with the pump housing at the cylinder chamber and the plunger. The rubber material of the main seal flows like a thick liquid during operation, which results in the pressure in the main seal to drop due to flow loss and wall friction loss. The lower pressure allows the higher pressure of the pumped fluid to flow around both sides of the main seal, causing it to hydraulically float and preventing seal formation. Instead, the seal assembly seals at narrow gaps formed between a ring adjacent the main seal and both the housing and the plunger. The pliant material of the main seal will flow into this gap, increasing the contact pressure between the elastomer and the walls of the recess. The contact pressure is higher than the pumping pressure, which causes the main seal to form a seal in the narrow gaps. The narrow gaps run the length of the adjacent ring. The narrow width of the gaps and the length of the extrusion into the gaps may exceed the pliant properties of the main seal, causing extreme fatigue and failure of the main seal, and ultimately failure of the pump. Thus, a seal assembly is needed that provides a seal between the plunger and the pump housing at the cylinder chamber while relieving stress and fatigue on the main seal to extend the life of the main seal and ultimately of the packing assembly.